Three electrode spark gap apparatus

ABSTRACT

A three electrode spark gap apparatus wherein three electrodes are arranged along the same axis with two of the electrodes concentrically arranged. The electrodes and the enclosure which houses the electrodes are generally cylindrical shaped and are dimensioned so that the radius of the enclosure is at least four times greater than the radius of the largest electrode located within the enclosure to prevent damage to the enclosure from the arc between electrodes.

I United States Patent 1 m1 3,715,614 Linkroum 1 Feb. 6, 1973 s41 THREEELECTRODE SPARK GAP v 2,799,804 7/1957 Biondi ..3l3/l98 x APPARATUSPrimary ExaminerAlfred L. Brody L H .Y. [75] Inventor Irving E inkroum,ancock, N Atwmey Raymond J. Eifler et a1 [73] Assignee: The BendixCorporation 22 Filed: Sept. 28, 1971 [571 ABSTRACT [21] Appl' No;184,381 A three electrode spark gap apparatus wherein three electrodesare arranged along the same axis with two of the electrodesconcentrically arranged. The elec- [52] US. Cl ..3l3/183, 3 l3/l98trodes and the enclosure which houses the electrodes are generallycylindrical h p and are dimensioned [58] Fleld of Search "3l3/l83315/349 so that the radius of the enclosure is at least four timesgreater than the radius of the largest electrode located [56] 1Reiergnces cued. within the enclosure to prevent damage to the enclo-UNITED STATES PATENTS sure from the are between electrodes. I

2,790,923 4/1957 'Gates ..3l3/l98 44 Claims, 5 Drawing Figures PAIENIEI]FEB 6 I975 FIGURE 2 FIGURE FIGURE 4 FIGURE 3 b LOAD STORAGE CAPACITORTRIGGER PULSE FIGURE 5 TIIREE ELECTRODE SPARK GAP APPARATUS BACKGROUNDOF THE INVENTION This invention relates to a gaseous conductor forcontrolling discharges of energy greater than 100 joules stored incapacitor. The invention is more particularly related to a gaseousconductor that includes three electrodes, one of which is a triggerelectrode that renders the gaseous conductor conductive to discharge thecapacitor.

In certain blasting operations such as those performed in tunnels andshaft mining, it is generally desirable to explode explosives with,electric blasting caps. Typically, the electric blasting caps aredetonated by electric energy which is receivedfrom a battery or ac powersource. Obviously, the most important aspect in blasting is the safetyof the people involved in the operations. Therefore, a most importantsafety feature of any blasting circuit is the electric or mechanicaldevice that isolates the explosives from the electrical energy that willbe used to detonate the explosives. Ex-

' amples of electrical systems for firing explosive bridge wire devicesor the like may be found in US. Pat. No. 3,417,306 to J. L. Kanak titledRegulated Voltage Capacitor Discharge Circuit and US. Pat. 2,950,4l9 toI. E. Linkroum titled Ignition Apparatus. In all of the prior artblasting circuits, the reliability and the life of the electricalelement that isolated the explosives from the electrical energy thatdetonated them was al ways a serious problem to work with. One devicewhich is utilized to isolate the explosives from the electricalcircuitry is a two or three electrode gaseous conductor called a sparkgap. In this device, one electrode trig- I gers the gaseous conductorconductive and establishes an are between the trigger electrode andcathode electrode that jumps to the anode electrode permitting the rapiddischarge of the stored energy in the capacitor. It is important thatthis device operates (conducts) properly every time it is triggered. Thespark gap includes a glass enclosure to allow for the observation of thearc discharge when it occurs. One problem with prior art spark gaps isthe are between the electrodes which blackens and melts the glass to apoint where it is questionable whether. or not the spark gap wouldoperate or even worse, would operate after an unknown time delay. Whendealing with explosives, this condition is too dangerous to permit.

SUMMARY OF THE INVENTION This invention provides a three electrode sparkgap device that is shaped and dimensioned to protect the glass enclosurearound the electrodes from unwanted material sputtered from the cathodeand heat from the are between the electrodes both of which could damagethe device and prevent proper operation of the spark gap.

The invention is a three electrode spark gap for capacitive dischargecircuits that is characterized by the physical sizes and the locationsof the components which optimize the life and operation of the device.

In one embodiment of the invention, the three electrode spark tapcomprises: an air-tight enclosure comprised of a glass tube having aKovar (T.M.) base mounted at each end of the tube to form the enclosure,the tube includes a central longitudinal axis and an inside radialcross-sectional area A4, the inside surface of the tube spaced from thecentral axis a minimum radial distance R4; an ionizable atmosphere, thatincludes argon, contained in the enclosure at a pressure less thanatmospheric; a first elongated electrode mounted on one base andextending into'the enclosure along the central axis, the free endportion of the first electrode including an arc discharge surface havinga cross-sectional area Al, the surface terminating from the central axisa maximum radial distance R1, which is less than R4, and wherein theRatio R4/Rl is greater than 4 and the ratio A4/Al is greater than 3; thesecond elongated electrode mounted on the other base and extending intothe enclosure along the central axis, the free end portion of the secondelectrode including an arc discharge surface which is spaced from andfaces the arc discharge surface of the first electrode and which has across-sectional area A2, which is less than A1 and which terminates amaximum radialdistance R2 from the central axis which is less than R1,the second electrode electrically isolated from the first electrode; anda third tubular electrode mounted on the said other base and extendinginto the enclosure along the central axis, the third tubular electrodeelectrically isolated from the first and second electrodes and mountedconcentric with the second electrode, said free end portion of saidthird electrode including an arch discharge surface which is spaced fromand faces the arc discharge surface of the first electrode and which hasa cross-sectional area A3, which is greater than A2, but less than A1,and which terminates a maximum radial distance R3, from the central axiswhich is greater that R1, and wherein the ratio R4/R3 is greater than 4.

Accordingly, it is an object of this invention to provide a threeelectrode spark gap for firing an explosive bridge wire device or thelike that is more reliable and has longer life than prior art devices.

Another object of this invention is to provide a device for triggeringexplosive devices.

Another object of this invention is improve the safety features ofexisting capacitor discharge devices for blasting applications.

It is still a further object of this invention to provide a triggerdevice for a capacitive discharge circuit that electrically isolatesenergy stored in the capacitor from a detonating device connected toexplosives.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings and claims which form a part of thisspecification.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTReferring now to the drawings, FIG. 1 illustrates a spark dischargedevice for triggering a capacitor discharge circuit. The spark gapdevice shown is used in blasting machine circuits and serves as a switchfor discharging the energy stored in .the capacitor through blastingcaps. This device has been found to begreatly superior to mechanicalswitches in this application because the contacts of mechanical switchesburn away after relatively few operations because of the energy passingthrough them. Ordinary gaseous conductors are inappropriate for usein-blasting machine applications because the discharge energy is high(greater than 100 joules). Therefore, the dimensions and materials usedin a spark gap device are very important.

FIG. 1 shows a spark gap device which comprises: an enclosure formed bybase platesS and 6, mounted'on the ends of the glass tube 4, andelectrodes 1, 2 and 3 mounted on the base plates 5 and 6 along thecentral or longitudinal axis X of the tube 4. Thetubing 4 is comprisedof a transparent material such as glass so that when an arc is initiatedin the enclosure, it may be observed. Because of the high temperaturesassociated air-tightenclosure. The enclosure may be evacuated by atubulation in the glass or by the tubulation 51 shown attached to thebase 5. The sealed enclosure is evacuated to a pressure below I X 10'torr and then backfilled with an ionizable atmosphere to a pressurebelow atmospheric. A preferred. ionizable atmosphere contains argon andis a mixture of 80 percent hydrogen and percent argon filled to apressure of about 350 X The cathode electrode 1, the anode electrode 3,and the trigger electrode 2 are comprised of materials chosen for theirelectrical and physical characteristics at high currents, voltages andtemperatures. Examples of acceptable electrode materials are molybdenum,tungsten,..thoriated tungsten and tungsten with a low work function(less than 4.5 electron volts) metal such as thorium, aluminum, bariumand mixtures thereof. In the preferred embodiment shown, the cathodeelectrode 1 is tungsten with barium aluminate, the anode 3 is comprisedof tungsten with barium aluminate, and the trigger electrode 2 ismolybdenum. Because of the high'energy associated with this are gapdischarge, tungsten is the electrode material for the anode and cathodebecause of its high temperature characteristics (high meltingtemperature). Barium aluminate is added to the tungsten to improve theelectrical characteristics of those electrodes as barium aluminateincreases the emissivity of electrodes. The trigger electrode 2 iscomprised of molybdenum because of its electrical and thermal expansionproperties.

For a detailed discussion of gaseous conductors see Vacuum Tube andSemi-Conductor Electronics,

Chapter 12 Electrical Discharges in Gases by Jacob Millman, published byMcGraw Hill and Gaseous Conductors," by James Cobine published by DoverPublications.

FIG. 2 is a cut-away view taken along lines Il-II of FIG. 1. The cathodeelectrode 1 includes a generally flat arc discharge surface .11. Thedischarge surface 11 has a total surface area A1, which extends apredetermined distance Rl from thecentral axis. Similarly, the

inner diameter borosilicate glass tubing 4 defines a radialcross-sectional area A4 that extendsa predetermined distance R4 from thecentral axis X. To adequately protect the borosilicate glass frommelting or receiving sputtered cathode material during the presence ofan arc discharge, the radial distance R4 of the inner wall of the glasstubing 4 is at least 4 times greater than the radial distance R1, whichis the terminal point of the discharge surface 11 of the cathode withinthe enclosure to trigger the device, this device employs a generallycylindrical molybdenum electrode having a cross-sectional areasufficient to handle-currents associated with discharges greater thanjoules. The trigger electrode 2 is isolated from the anode electrode 3by an insulating sleeve 22. The insulating sleeve 22 is brazed withcopper base brazing material 23 to the trigger electrode 32 to make theconnection air tight. So that the starting characteristics of the'sparkdischarge are optimized, the trigger discharge surface 21 extends beyondthe end of the anode surface 31. As can be seen from the drawing, theanode electrode 3 is generally tubular shaped and mountedconcentricallyv with the trigger electrode 2. The free end portion ofthe anode electrode 3 is comprised of a tungsten material with bariumaluminate. The anode 3 is also brazed to the insulator 22 by a copperbased alloy 33. The member 35 that extends from the anode 3 is anelectrical conducting member for attaching the anode to a capacitivecircuit. To assure .the anode electrode 3 is mounted inair-tight'relationship to the base 6, it is brazed to the base 6 with acopper base alloy 33. FIG. 4 is an end view of the electrode shown inFIG. 3 taken along lines IV-IV. This view shows the physicalrelationships between the anode electrode 3 and the trigger electrode 2.The trigger electrode 2 .is mounted concentric with the central axis Xand terminates in an arc discharge'surface 21. The discharge surface 21has a predetermined cross-sectional area-A2, which extends a radialdistance R2 from the central axis X. The anode electrode 3 is mountedconcentric with the central axis X and the trigger electrode 2 andterminates in an arc discharge surface 31. The anode arc dischargesurface 31 has a predetermined surface area A3, which extends a radialdistance R3 from the central axis. The radius- R3 is dimensioned so thatthe ratio R4/R3 is greater than 4. This assures that the envelope 4(FIG. 2) will be adequately protected from the heat generated by anarcbetween the electrodes.

FIG. 5 shows schematically how the trigger discharge device is used. Thespark discharge device has its anode 3 connected to a source of storedenergy such as a positive terminal of a charged capacitor, its anodeelectrodel connected to a load, and the trigger electrode 2 connected toa means for receiving a trigger pulse 71, 72 and a resistor 73.

In operation, the spark gap discharge device would operate as follows:When a trigger pulse is applied to the trigger electrode 2 an electricarc is initiated between the trigger electrode 2 and the cathode 1. Thevalue of the trigger pulse necessary to initiate this arc is a functionof the voltage between the electrodes the electrode materials, thespacing between electrodes, the gas in the enclosure, and the pressureof the gas within the enclosure. Once an arc is established between thetrigger electrode 2 and the cathode 1, the energy stored in the storagecapacitor begins to discharge through the arc and to the load. However,the current limiting resistor 73 begins to limit the current through thetrigger electrode so that the arc, looking for the path of leastresistance, jumps to the arc discharge surface 31 of the anode electrode3. The energy in the storage capacitor is then discharged through theblasting caps which explode the dynamite.

The following information summarizes the pertinent details in assemblinga preferred embodiment of the invention.

EXAMPLE I Part Size Material (4) Tubing lD 2.025 Borosilicate OD 2.250Glass (5) (6) Bases OD 2.030 Kovar (11) Cathode discharge surface OD.2666 Tungsten combined with a low work function metal (21) Anode ID.430 Tungsten with a low work function material discharge surface OD.4375 (31) Trigger discharge surface OD .125 Molybdenum Spacingbetweencathode and trigger: 0.135 Spacing between cathode and anode:0.165 Gas Fill: 80% H and 20% A to 350 X torr Breakdown voltage(cathode-trigger): 3700 3800 volts DC Electrodes mounted on bases withcopper brazing material Trigger voltages3KV While a preferred embodimentof the invention has been disclosed, it will be apparent to thoseskilled in the art that changes may be made to the invention as setforth in the appended claims, and, in some cases, certain features ofthe invention may be used to advantage without corresponding use ofother features. For example, the electrodes and enclosure may takeshapes other than cylindrical so long as the maximum radial distancewhich the discharge surfaces of'the electrodes extend from the centralaxis is in the proper ratio to the minimum radial distance that theinner wall of the enclosure is spaced from the central axis.Accordingly, it

is intended that the illustrative and descriptive materials herein beused to illustrate the principles of the invention and not to limit thescope thereof.

Having described the invention, what is claimed is:

l. A three electrode spark gap comprising:

an air-tight enclosure comprised of a tube having a first base mountedatone end of said tube and a second base mounted at the other end ofsaid tube to form said enclosure, said tube having a central axis and aninside radial cross-sectional area A4, said inside surface of said tubespaced from said central axis a minimum radial distance R4;

an ionizable atmospherecontained in said enclosure;

a first electrode mounted on said first base and extending into saidenclosure along said central axis, said free end portion of said firstelectrode including an arc discharge surface area Al, said surfaceterminating from said central axis a maximum radial distance R1, whichis less than R4 and wherein the ratio R4/R1 is greater than 4;

a second electrode mounted on said second base and extending into saidenclosure along said central axis, said free end portion of said secondelectrode including an arc discharge surface area A2 which is spacedfrom and faces the arc discharge surface of said first electrode, whichis less than A1, and which terminates a maximum radial distance R2 fromsaid central axis which is less than R1, said second electrodeelectrically isolated from said first electrode; and I a third tubularelectrode mounted on said second base and extending into said enclosurealong said central axis, said third tubular electrodeelectricallyisolated from said first and second electrodes and mounted concentricwith said second electrode, said free end portion of said thirdelectrode including an arc discharge surface area A3 which is spacedfrom and faces the arc discharge surface of said first electrode andwhich terminates a maximum radial distance R3 from said central axiswhich is greater than R2, and wherein the. ratio R4/R3 is greater than4.

2. The three electrode spark gap as recited in claim 1 wherein thesurface area A3 terminates a maximum radial distance R3 from saidcentral axis which is greater than Rl.

3. The three electrode spark gap is recited in claim 2 wherein thesurface area A3 is greater than the surface area A2.

4. The three electrode spark gap as recited in claim] wherein the arcdischarge surface of said third electrode is spaced further from the arcdischargesurface of said first electrode than said second arc dischargesurface.

5. The three electrode spark gap as recited in claim 2 wherein the arcdischarge surface of said third electrode is spaced further from the arcdischarge surface of said first electrode than said second arc dischargesurface. I

6. The three electrode spark gap as recited in claim 3 .wherein the arcdischarge surface of said third electrode is spaced further from the arcdischarge surface of said first electrode than said second arc dischargesurface.

7. The three electrode spark gap as recited in claim 1 wherein saidairtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of aheat resistanttransparent tube whereby the occurrence of an electric arc between thearc discharge surfaces can be observed.

8. The three electrode spark gap as recited in claim 2 wherein saidairtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of a heat resistanttransparent tube whereby the occurrence of an electric are between thearc discharge surfaces can be observed.

9. The three electrode spark gap as recited in claim 3 wherein saidairtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of a heat resistanttransparent tube whereby the occurrence of an electric are between thearc discharge surfaces can be observed.

10. The three electrode spark gap as recited in claim 4 wherein saidairtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of a heat resistanttransparent tube whereby the occurrence of an electric are between thearc discharge surfaces can be observed.

11. The three electrode spark gap as recited in claim 5 wherein said.airtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of a heat resistanttransparent tube'whereby the occurrence of an electric are between thearc discharge surfaces can be observed.

12. The three electrode spark gap as recited in claim 6 wherein saidairtight enclosure includes:

means for spacing said first and second bases from each other apredetermined distance, said spacing means comprised of a heat resistanttransparent tube whereby the occurrence of an electric arc between thearc discharge surfaces can be observed.

13. A three electrode spark gap as recited in claim 1 wherein thepressure in said enclosure is less than 750 X 10- torr and includes amixture of hydrogen and Argon.

14. A three electrode spark gap as recited in claim 2 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

15. A three electrode spark gap as recited in claim 3 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

16. A three electrode spark gap as recited in claim'4 wherein thepressure in said enclosure is less than 750 X 10' torr and. includes amixture of hydrogen and Argon. r r

17. A three electrode spark gap as recited in claim 5 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

18. A three electrode spark gap as recited in claim 6 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

19. A three electrode spark gap as recited in claim 7 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

20. A three electrode spark gap as recited in claim 8 wherein thepressure in said enclosure is less than 750 I X 10' torr and includes amixture of hydrogen and Argon.

21. A three electrode spark gap as recited in claim 9 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

22. A three electrode spark gap as recited in claim 10 wherein thepressure in said enclosure is less than-750 X 10' torr and includes amixture of hydrogen and Argon.

23. A three electrode spark gap as recited in claim 1 1 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

24. A three electrode spark gap as recited in claim 12 wherein thepressure in said enclosure is less than 750 X 10' torr and includes amixture of hydrogen and Argon.

25. A three electrode spark gap as recited in claim 1 wherein said aredischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

26. A three electrode spark gap as recited in claim 2 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

27. A three electrode spark gap as recited in' claim 3 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

28. A three electrode spark gap as recited in claim 4 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

29. A three electrode spark gap as recited in claim 7 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

30. A three electrode spark gap as recited in claim 8 wherein said aredischarge surfaces of said second and third electrodes are comprised'ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

31. A three electrode spark gap as recited in claim 9 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

32. A three electrode spark gap as recited in claim 13 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

33. A three electrode spark gap as recited in claim 14 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

34. A three electrode spark gap as recited in claim 15 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

35. A three electrode spark gap as recited in claim 16 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.

36. The three electrode spark gap as recited in claim 1 wherein thefirst base and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X10- to 0.5 X 10' so that glass may be sealed to said bases withoutcracking.

37. The three electrode spark gap as recited in claim 7 wherein thefirst base and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X10' to 0.5 X 10- so that glass may be sealed to said baseswithoutcracking.

38. The three electrode spark gap as recited in claim 8 wherein thefirst base and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X10' to 0.5 X 10- so that glass may be sealed to said baseswithoutcracking.

39. The three electrode spark gap as recited in claim 9 wherein thefirst base and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X10' to 0.5. X 10" so that glass may be sealed to said bases withoutcracking. r 40. The three electrode spark gap as recited in claim 10wherein the first base and second base of said enclosure are comprisedof a material having a coefficient of linear thermal "expansion intherange of 50 X 10' to 0.5 X 10' so that glass may be sealed to said baseswithout cracking.

41. The three electrode spark gap as recited in claim 11 wherein thefirst base'and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X10' to 0.5 X 10' sothat glass, may be sealed to said bases withoutcracking.

'42. The three electrode spark gap as recited in claim 12 wherein thefirst base and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X 10to 0.5 X 10 so that glass may be sealed to said bases without cracking.

43. A three electrode spark gap comprising: an air-tight enclosurecomprised of a glass tube having a first base mounted at one end of.said tube and a second base mounted at the other end of said tube toform said enclosure said first base and said second base having acoefficient of linear thermal expansion in the range of 50 X 10', to 0.5X 10", said tube having a central axis and an inside radialcross-sectional area A4, said inside surface of said tube spaced fromsaid central axis a radial distance R4;

an ionizablc atmosphere that includes Argon contained in said enclosure,said pressure within said enclosure less than 750 X l0" torr;

a first elongated electrode mounted on said first base and extendinginto said enclosure along said central axis, said free end portion ofsaid first electrode including an arc discharge surface having across-sectional area Al, said surface terminating from said central axisa radial distance R] which is less than R4, and wherein said ratio R4/Rlis greater than 4 and the ratio A4/Al is greater than second elongatedelectrode mounted on said second base and extending into said enclosurealong said central axis; said free end portion of said second electrodeincluding an arc discharge surface which is spaced from and faces thearc discharge surfaces of said first electrode and which has across-sectional area A2, which is less than Al, and which terminates aradial distance R2 from said central axis which is less than R1, saidsecond electrode electrically isolated from said first electrode; and

a third tubular electrode mounted on said second base and extending intosaid enclosure along said central axis, said third tubular electrodeelectrically isolated from said first and second electrodes and mountedconcentric with said second electrode, said free end portion of saidthird electrode including an arc discharge surface which is spaced fromand faces the arc discharge surface of said first electrode and whichhas a cross-sectional area A3 which is greater than A2, less than 1, andterminates a radial distance R3 from said central axis which is greaterthan R1, and wherein the ratio R4/R3 is greater than 4.

44. The three electrode spark gap as recited in claim 1 wherein said aredischarge'surfaces of said first and third electrodes are comprised ofbarium aluminate.

1. A three electrode spark gap comprising: an air-tight enclosurecomprised of a tube having a first base mounted at one end of said tubeand a second base mounted at the other end of said tube to form saidenclosure, said tube having a central axis and an inside radialcross-sectional area A4, said inside surface of said tube spaced fromsaid central axis a minimum radial distance R4; an ionizable atmospherecontained in said enclosure; a first electrode mounted on said firstbase and extending into said enclosure along said central axis, saidfree end portion of said first electrode including an arc dischargesurface area A1, said surface terminating from said central axis amaximum radial distance R1, which is less than R4 and wherein the ratioR4/R1 is greater than 4; a second electrode mounted on said second baseand extending into said enclosure along said central axis, said free endportion of said second electrode including an arc discharge surface areaA2 which is spaced from and faces the arc discharge surface of saidfirst electrode, which is less than A1, and which terminates a maximumradial distance R2 from said central axis which is less than R1, saidsecond electrode electrically isolated from said first electrode; and athird tubular electrode mounted on said second base and extending intosaid enclosure along said central axis, said third tubular electrodeelectrically isolated from said first and second electrodes and mountedconcentric with said second electrode, said free end portion of saidthird electrode including an arc discharge surface area A3 which isspaced from and faces the arc discharge surface of said first electrodeand which terminates a maximum radial distance R3 from said central axiswhich is greater than R2, and wherein the ratio R4/R3 is greater than4.
 1. A three electrode spark gap comprising: an air-tight enclosurecomprised of a tube having a first base mounted at one end of said tubeand a second base mounted at the other end of said tube to form saidenclosure, said tube having a central axis and an inside radialcross-sectional area A4, said inside surface of said tube spaced fromsaid central axis a minimum radial distance R4; an ionizable atmospherecontained in said enclosure; a first electrode mounted on said firstbase and extending into said enclosure along said central axis, saidfree end portion of said first electrode including an arc dischargesurface area A1, said surface terminating from said central axis amaximum radial distance R1, which is less than R4 and wherein the ratioR4/R1 is greater than 4; a second electrode mounted on said second baseand extending into said enclosure along said central axis, said free endportion of said second electrode including an arc discharge surface areaA2 which is spaced from and faces the arc discharge surface of saidfirst electrode, which is less than A1, and which terminates a maximumradial distance R2 from said central axis which is less than R1, saidsecond electrode electrically isolated from said first electrode; and athird tubular electrode mounted on said second base and extending intosaid enclosure along said central axis, said third tubular electrodeelectrically isolated from said first and second electrodes and mountedconcentric with said second electrode, said free end portion of saidthird electrode including an arc discharge surface area A3 which isspaced from and faces the arc discharge surface of said first electrodeand which terminates a maximum radial distance R3 from said central axiswhich is greater than R2, and wherein the ratio R4/R3 is greater than 4.2. The three electrode spark gap as recited in claim 1 wherein thesurface area A3 terminates a maximum radial distance R3 from saidcentral axis which is greater than R1.
 3. The three electrode spark gapis recited in claim 2 wherein the surface area A3 is greater than thesurface area A2.
 4. The three electrode spark gap as recited in claim 1wherein the arc discharge surface of said third electrode is sPacedfurther from the arc discharge surface of said first electrode than saidsecond arc discharge surface.
 5. The three electrode spark gap asrecited in claim 2 wherein the arc discharge surface of said thirdelectrode is spaced further from the arc discharge surface of said firstelectrode than said second arc discharge surface.
 6. The three electrodespark gap as recited in claim 3 wherein the arc discharge surface ofsaid third electrode is spaced further from the arc discharge surface ofsaid first electrode than said second arc discharge surface.
 7. Thethree electrode spark gap as recited in claim 1 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 8. The threeelectrode spark gap as recited in claim 2 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 9. The threeelectrode spark gap as recited in claim 3 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 10. The threeelectrode spark gap as recited in claim 4 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 11. The threeelectrode spark gap as recited in claim 5 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 12. The threeelectrode spark gap as recited in claim 6 wherein said airtightenclosure includes: means for spacing said first and second bases fromeach other a predetermined distance, said spacing means comprised of aheat resistant transparent tube whereby the occurrence of an electricarc between the arc discharge surfaces can be observed.
 13. A threeelectrode spark gap as recited in claim 1 wherein the pressure in saidenclosure is less than 750 X 10 3 torr and includes a mixture ofhydrogen and Argon.
 14. A three electrode spark gap as recited in claim2 wherein the pressure in said enclosure is less than 750 X 10 3 torrand includes a mixture of hydrogen and Argon.
 15. A three electrodespark gap as recited in claim 3 wherein the pressure in said enclosureis less than 750 X 10 3 torr and includes a mixture of hydrogen andArgon.
 16. A three electrode spark gap as recited in claim 4 wherein thepressure in said enclosure is less than 750 X 10 3 torr and includes amixture of hydrogen and Argon.
 17. A three electrode spark gap asrecited in claim 5 wherein the pressure in said enclosure is less than750 X 10 3 torr and includes a mixture of hydrogen and Argon.
 18. Athree electrode spark gap as recited in claim 6 wherein the pressure insaid enclosure is less than 750 X 10 3 torr and includes a mixture ofhydrogen and Argon.
 19. A three electrode spark gap as recited in claim7 wherein the pressure in said enclosure is less than 750 X 10 3 torrand includes a mixture of hydrogen and Argon.
 20. A three electrodEspark gap as recited in claim 8 wherein the pressure in said enclosureis less than 750 X 10 3 torr and includes a mixture of hydrogen andArgon.
 21. A three electrode spark gap as recited in claim 9 wherein thepressure in said enclosure is less than 750 X 10 3 torr and includes amixture of hydrogen and Argon.
 22. A three electrode spark gap asrecited in claim 10 wherein the pressure in said enclosure is less than750 X 10 3 torr and includes a mixture of hydrogen and Argon.
 23. Athree electrode spark gap as recited in claim 11 wherein the pressure insaid enclosure is less than 750 X 10 3 torr and includes a mixture ofhydrogen and Argon.
 24. A three electrode spark gap as recited in claim12 wherein the pressure in said enclosure is less than 750 X 10 3 torrand includes a mixture of hydrogen and Argon.
 25. A three electrodespark gap as recited in claim 1 wherein said arc discharge surfaces ofsaid second and third electrodes are comprised of different materialsand said first and third electrodes are comprised of the same materials.26. A three electrode spark gap as recited in claim 2 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.
 27. A three electrode spark gap as recited in claim3 wherein said arc discharge surfaces of said second and thirdelectrodes are comprised of different materials and said first and thirdelectrodes are comprised of the same materials.
 28. A three electrodespark gap as recited in claim 4 wherein said arc discharge surfaces ofsaid second and third electrodes are comprised of different materialsand said first and third electrodes are comprised of the same materials.29. A three electrode spark gap as recited in claim 7 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.
 30. A three electrode spark gap as recited in claim8 wherein said arc discharge surfaces of said second and thirdelectrodes are comprised of different materials and said first and thirdelectrodes are comprised of the same materials.
 31. A three electrodespark gap as recited in claim 9 wherein said arc discharge surfaces ofsaid second and third electrodes are comprised of different materialsand said first and third electrodes are comprised of the same materials.32. A three electrode spark gap as recited in claim 13 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.
 33. A three electrode spark gap as recited in claim14 wherein said arc discharge surfaces of said second and thirdelectrodes are comprised of different materials and said first and thirdelectrodes are comprised of the same materials.
 34. A three electrodespark gap as recited in claim 15 wherein said arc discharge surfaces ofsaid second and third electrodes are comprised of different materialsand said first and third electrodes are comprised of the same materials.35. A three electrode spark gap as recited in claim 16 wherein said arcdischarge surfaces of said second and third electrodes are comprised ofdifferent materials and said first and third electrodes are comprised ofthe same materials.
 36. The three electrode spark gap as recited inclaim 1 wherein the first base and second base of said enclosure arecomprised of a material having a coefficient of linear thermal expansionin the range of 50 X 10 6 to 0.5 X 10 6 so that glass may be sealed tosaid bases without cracking.
 37. The three electrode spark gap asrecited in claim 7 wherein the first base and second base of saidenclosure are comprised of a material having a coefficient of linearthermal expansion in the range of 50 X 10 6 to 0.5 X 10 6 so that glassmay be sealed to said bases without cracking.
 38. The three electrodespark gap as recited in claim 8 wherein the first base and second baseof said enclosure are comprised of a material having a coefficient oflinear thermal expansion in the range of 50 X 10 6 to 0.5 X 10 6 so thatglass may be sealed to said bases without cracking.
 39. The threeelectrode spark gap as recited in claim 9 wherein the first base andsecond base of said enclosure are comprised of a material having acoefficient of linear thermal expansion in the range of 50 X 10 6 to 0.5X 10 6 so that glass may be sealed to said bases without cracking. 40.The three electrode spark gap as recited in claim 10 wherein the firstbase and second base of said enclosure are comprised of a materialhaving a coefficient of linear thermal expansion in the range of 50 X 106 to 0.5 X 10 6 so that glass may be sealed to said bases withoutcracking.
 41. The three electrode spark gap as recited in claim 11wherein the first base and second base of said enclosure are comprisedof a material having a coefficient of linear thermal expansion in therange of 50 X 10 6 to 0.5 X 10 6 so that glass may be sealed to saidbases without cracking.
 42. The three electrode spark gap as recited inclaim 12 wherein the first base and second base of said enclosure arecomprised of a material having a coefficient of linear thermal expansionin the range of 50 X 10 6 to 0.5 X 10 6 so that glass may be sealed tosaid bases without cracking.
 43. A three electrode spark gap comprising:an air-tight enclosure comprised of a glass tube having a first basemounted at one end of said tube and a second base mounted at the otherend of said tube to form said enclosure, said first base and said secondbase having a coefficient of linear thermal expansion in the range of 50X 10 6, to 0.5 X 10 6, said tube having a central axis and an insideradial cross-sectional area A4, said inside surface of said tube spacedfrom said central axis a radial distance R4; an ionizable atmospherethat includes Argon contained in said enclosure, said pressure withinsaid enclosure less than 750 X 10 3 torr; a first elongated electrodemounted on said first base and extending into said enclosure along saidcentral axis, said free end portion of said first electrode including anarc discharge surface having a cross-sectional area A1, said surfaceterminating from said central axis a radial distance R1 which is lessthan R4, and wherein said ratio R4/R1 is greater than 4 and the ratioA4/A1 is greater than 3; a second elongated electrode mounted on saidsecond base and extending into said enclosure along said central axis,said free end portion of said second electrode including an arcdischarge surface which is spaced from and faces the arc dischargesurfaces of said first electrode and which has a cross-sectional areaA2, which is less than A1, and which terminates a radial distance R2from said central axis which is less than R1, said second electrodeelectrically isolated from said first electrode; and a third tubularelectrode mounted on said second base and extending into said enclosurealong said central axis, said third tubular electrode electricallyisolated from said first and second electrodes and mounted concentricwith said second electrode, said free end portion of said thirdelectrode including an arc discharge surface which is spaced from andfaces the arc discharge surface of said first electrode and which has across-sectional area A3 which is greater than A2, less than 1, andterminates a radial distancE R3 from said central axis which is greaterthan R1, and wherein the ratio R4/R3 is greater than 4.